Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $228.99   13.543%   $260.0021   $260.00   $260.00   $260.00  
  Purchase #2 $239.73   13.394%   $271.8394   $271.84   $271.85   $271.80  
  Purchase #3 $69.41   11.847%   $77.633   $77.63   $77.65   $77.60  
  Purchase #4 $10.70   6.607%   $11.4069   $11.41   $11.40   $11.40  
  Purchase #5 $17.26   3.763%   $17.9095   $17.91   $17.90   $17.90  
  Purchase #6 $235.56   13.517%   $267.4006   $267.40   $267.40   $267.40  
  Purchase #7 $203.35   8.595%   $220.8279   $220.83   $220.85   $220.80  
  7 purchase totals = $1,005.00       $1,127.0194   $1,127.02   $1,127.05   $1,126.90